A coker or coker unit is an oil refinery processing unit which converts residual feed oil from a vacuum distillation column into low molecular weight hydrocarbon gases, naphtha, light and heavy gas oils, and petroleum coke. The process thermally cracks long chain hydrocarbon molecules in a residual oil feed into shorter chain molecules leaving behind the excess carbon in the form of petroleum coke. A delayed coker is a particular type of coker unit where the process comprises heating the residual oil feed to its thermal cracking temperature in a multi-parallel pass furnace which thermally cracks the long chain heavy carbon and hydrogen molecules of the residual oil into coker gas oil and petroleum coke.
Cracking begins in the coker furnace which includes a heater, where there are multiple coke drums, with a coker furnace for each pair of coke drums. The coker fractionator receives feedstock directly from the coke drum and separates the feedstock and sour ‘cracked’ gas and liquids from the coke drum.
Refiners worldwide seek to increase the liquid product yield from existing delayed coking units. For a particular recycle ratio (fresh feed+recycle)/fresh feed) and feed continuous catalyst regeneration (CCR) content the coke yield is normally proportional to the operating column pressure of the coke drum. The lower the operating column pressure in the coke drum the better the liquid yield.